GC-MS & GC-IMS Reveal Black Tea Aroma Secrets

Because the time of fermentation time and first drying temperature play crucial roles in the quality of black tea flavor, a joint study made up of researchers from Zhejiang Agriculture and Forestry University (Hangzhou, China), the Agricultural Industrialization Development Center of Ninghai County (Ningbo, China) and the College of Agriculture and Food Sciences at King Faisal University (Al-Ahsa, Saudi Arabia) investigated their combined effects on biochemical and volatile compounds (VOCs) in two cultivars. The team used gas chromatography-mass spectrometry (GC-MS) and gas chromatography-ion mobility spectrometry (GC-IMS) to identify the VOCs. A paper based on their efforts was published in Food Chemistry: X.¹

Why Are Fermentation and Drying Important in Ensuring a Quality-Flavored Tea?

Black tea makes up around 75% of all the tea drunk worldwide, making it one of the most popular non-alcoholic beverages on the planet. People love it not just for its bold, distinctive taste, but also for the good it does for the body — from helping manage blood sugar and fighting off harmful bacteria to being packed with antioxidants.² The quality of black tea comes down to a number of things — the type of tea plant used, the environment it's grown in, how it's processed, and the conditions under which it's stored.³

Fermentation is one of the most important steps in making black tea. During this stage, natural enzymes in the tea leaves trigger a series of chemical reactions that break down certain compounds found in the leaves. This process gives rise to a group of color-producing substances — theaflavins, thearubigins, and theabrownins — which are largely responsible for black tea's rich color and distinctive taste.⁴

Once fermentation is complete, drying plays a crucial role in determining the final quality of the tea. The heat from drying essentially "switches off" the fermentation process by deactivating the enzymes responsible for it. This locks in all the chemical changes that have taken place, while also drawing out most of the moisture from the leaves — bringing it down to just 3–4%. The result is a better-tasting tea that also stays fresh for longer.⁵

The authors of the paper state that, while previous research has looked at how fermentation time and drying temperature each separately influence the way black tea tastes, how the two work together to affect the final quality of the tea hasn't really been examined. For this study, they wanted to explore how different combinations of fermentation times (2.5, 4, and 5.5 hours) and drying temperatures (95 °C, 110 °C, and 125 °C) affect the overall quality of black tea made from two different tea varieties: Wanghai-1 (grown from cuttings) and JiuKeng (grown from seeds). To get a full picture, they looked at how the tea tasted and smelled, measured its key chemical components, and used specialized techniques to identify the aroma compounds responsible for its flavor. Ultimately, they believe that this research will help lay the groundwork for fine-tuning the tea-making process to consistently produce better-quality black tea, with practical takeaways that could also be applied at a larger, commercial scale.¹

How Do Fermentation Time and Drying Temperature Work Together to Shape the Flavor and Quality of Black Tea?

A 2.5-hour fermentation step followed by initial drying at 95 °C was found to be important for developing aroma, since longer fermentation and higher drying temperatures reduced aroma quality. Extended processing also lowered levels of free amino acids, reducing sugars, and theaflavin. GC–MS analysis identified 92 volatile compounds, mainly alcohols and aldehydes. Important aroma contributors included cedrol, nonanal, trans-beta-ionone, and phenylacetaldehyde, which added woody, floral, and honey-like notes. Although the two tea cultivars showed different metabolic profiles, the processing conditions caused similar directional changes in both.¹

“This study, write the authors of the paper,¹ “provides new insight into dynamic variations driven by combined effect of processing parameters in different cultivars.”

The researchers believe that future studies should look at tea samples from different seasons and regions, along with a wider variety of processing methods, to see if these results apply more broadly.¹

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References

1. Yasir, M.; Jiang, Y.; Walayat, N. et al. Exploring the Combined Effect of Fermentation Time, and First Drying Temperature on Black Tea Flavor Profile Characterized by GC-MS and GC-IMS. Food Chem X 2026, 36, 103975. DOI: 10.1016/j.fochx.2026.103975
2. Su, S.; Long, P.; Zhang, Q. et al. Chemical, Sensory and Biological Variations of Black Tea Under Different Drying Temperatures. Food Chem. 2024, 446, 138827. DOI: 10.1016/j.foodchem.2024.138827
3. Zheng, X. Q.; Li, Q. S.; Xiang, L. P. et al. Recent Advances in Volatiles of Teas. Molecules 2016, 21 (3), 338. DOI: 10.3390/molecules21030338
4. Xiao, Y.; Li, M.; Wu, Y. et al. Structural Characteristics and Hypolipidemic Activity of Theabrownins from Dark Tea Fermented by Single Species Eurotium cristatum PW-1. Biomolecules 2020, 10 (2), 204. DOI: 10.3390/biom10020204
5. Vargas, R.; Vecchietti, A. Influence of Raw Material Moisture on the Synthesis of Black Tea Production Process. Journal of Food Engineering 2016, 173, 76-84. DOI: 10.1016/j.jfoodeng.2015.10.043